In recent years an image forming device using a toner system as exemplified by a laser printer has been widely used to make it possible to produce clear images with excellent resolution. Among the image forming devices using a toner system, as mentioned in the above, there are signs of change with the advent of models that can handle color images.
A description will be made of a prior art image forming device for forming color images.
FIG. 9 is a perspective view of a prior art image forming device that is in a state of performing an image transferring process. In FIG. 9, a photosensitive belt 101 is one form of the toner image transporting members and is coated with a layer of an organic photoconductive material on the surface thereof. The photosensitive belt 101 thus prepared rotates in the direction indicated by an arrow, thereby an image in each respective color out of the four primary colors, i.e., cyan, magenta, yellow and black, being formed in succession. Next, a series of the steps for forming color images will be described.
The photosensitive belt 101, the surface of which is uniformly charged to about -600 V by a charging means, is irradiated with laser light according to image signals from a light exposure making means 102 constructed by such an optical system as a laser irradiation unit, a polygon mirror and the like. The surface potential of the area exposed to the laser light is raised to around -100 V and an electrostatic latent image is formed on the surface of the photosensitive belt 101. An image developing means 103 is formed of four sections for each respective primary color, i.e., an image developing means 103C for cyan, an image developing means 103M for magenta, an image developing means 103Y for yellow and an image developing means 103B for black, each performing an image developing process for one color out of the four primary colors by the use of primary color toner contained in each respective section of the above.
For example, when an image developing process for an image in cyan is performed, a development roller of the image developing means 103C attached with negatively charged toner is pressed onto the photosensitive belt 101 to convert the electrostatic latent image into a visible image, transferring toner onto the surface of the photosensitive belt 101 in an area, where the electrostatic latent image has been formed. Thus, a toner image in cyan is formed. Then, the toner image in cyan formed on the photosensitive belt 101 is transferred onto an intermediate image transferring member 104. After the above image transferring, the toner that has remained on the surface of the photosensitive belt 101 is eliminated by a cleaning means.
A series of the foregoing steps are repeatedly performed for cyan, magenta, yellow and black in this order and a colored toner image 105 with the four primary colors combined is formed on the intermediate image transferring member 104. Then, the toner image 105 formed on the surface of the intermediate image transferring member 104 is transferred onto a printing paper 107 via pressure from the image transferring roller 106. At this time, the intermediate image transferring member 104 is rotated in the direction, in which the printing paper 107 is transported.
After the image transferring, the toner having remained on the intermediate image transferring member 104 is eliminated by a cleaning means. Finally, an image fixing means 108 places the printing paper 107 transferred with the toner image 105 between a pressure applying roller 109 and a heat applying roller 110 provided with a heat source inside, thus having a color image fixed onto the printing paper 107 by fusing toner particles into place.
However, the prior art image forming device as described in the above requires without fail the intermediate image transferring member 104 in order to form a color image and the size of the device is made large and the mechanism is made complex, resulting in an increase of component counts just because of the existence of the intermediate image transferring member 104, thereby making it difficult to reduce the size of the image forming device.